JOHN H. RYTHER 403 



The maximum concentration of phosphorus in the deep offshore 

 waters of the Caribbean ( 2 microgram atoms per hter ) , as determined 

 by Rakestraw and Smith ( 1937 ) , does not approach the maximum 

 observed in the red water patches (20 microgram atoms per hter), so 

 upwelhng could not have provided sufficient enrichment to be an 

 important factor. It is also unlikely that land drainage could account 

 for this phosphorus. Since the red water region contained only about 

 10% freshwater, runoff would have to carry tremendous concentrations 

 of this element to account for the amount present in the organisms 

 (estimated at 17,000 lb of pure phosphorus per square mile of red 

 water ) . Chew ( 1953 ) , who investigated a minor outbreak of red 

 water in the same region in 1952, found that the lower salinity, 

 coastal water, which contained the river drainage, had lower con- 

 centrations of phosphorus than the open waters of the Gulf of 

 Mexico. 



Thus it would appear that there may be insufficient nutrients 

 normally present in sea water, and no known mechanism for concen- 

 trating them to a sufficiently high level, to support the development 

 of a typcial red tide. The remaining possibility, that the organisms 

 themselves become concentrated after growth, will be discussed 

 below. 



In every case in which the vertical distribution of dinoflagellates 

 in red water has been examined, it was found that the organisms were 

 concentrated in relatively narrow bands usually at the surface of the 

 water ( Whitelegge, 1891; Nishikawa, 1901; Hirasaka, 1922; Martin 

 and Nelson, 1929). In three instances of small, local outbreaks of red 

 water, cell counts were made in a vertical column, revealing in each 

 case that the maximum concentration of dinoflagellates occurred at 

 the surface (Table III). 



It is very doubtful that the organisms could have grown in such a 

 pattern of distribution. As pointed out above, there would appear to 

 be insufficient nutrients available to support such populations. Fur- 

 thermore the high light intensities at the surface of the ocean are 

 normally inhibitory to photosynthesis (Stanbury, 1931; Jenkin, 1937), 

 particularly in the case of dinoflagellates, many of which appear to 

 prefer reduced illumination (Barker, 1935; King, 1950). Hence, dense 

 aggregations of dinoflagellates at the surface of the water must be 



